1. Field
This application relates generally to computer graphics and, more specifically, to the deformation of skin on a computer-generated character in computer animation.
2. Related Art
In the field of computer animation, a computer-generated character is typically modeled using a character rig having a skeleton structure covered with a skin layer that moves, or deforms, in response to movements of the skeleton structure. Animators may then animate the character by manipulating the positions of the bones and joints of the character's rig. Animating characters in this way can be more computationally efficient than the use of, for example, multiple individual drawings to produce an animation.
Since the skin layer of a computer-generated character is outwardly visible to viewers of the computer animation, efficient deformation techniques that produce convincing skin deformations are desirable. For example, if an animator chooses to bend the elbow of a computer-generated character, it would be desirable to deform the skin layer with a life like bulge at the biceps with minimal input from the animator and with minimal use of computing resources.
One deformation system that may be used to simulate skin deformations is the multipoint offset sampling (MOS) deformation system. In this system, the skin deformation of a character may be computed using hierarchically structured data types. In particular, the skeletal structure of a character may be represented by MOS transforms (e.g., representing joints of a character's body) connected together by implicit vectors (e.g., bones of the character's body). The MOS transforms may be associated with and control MOS vertices such that the positions of the MOS vertices are defined by the positions and orientations of the MOS transforms. The MOS vertices may in turn define the shapes and positions of MOS curves that are connected to skin vertices located on, adjacent to, or otherwise associated with the surface of a character's skin. The positions of the skin vertices relative to their connected MOS curves may depend on the orientations of associated MOS transforms.
The process that moves skin vertices relative to their associated MOS curves may be referred to as a “skin deformation.” Example skin deformation operations include bulge, slide, and twist operations. A character rigger may apply varying levels of these skin deformation operations to select skin vertices of a character rig to produce desired skin deformations when the positions of the MOS transforms are manipulated.
While conventional MOS deformation systems can be used to produce realistic animations, these systems typically include rigid assumptions that limit the rigger's ability to efficiently and intuitively model the appearance of a character's skin.